WASHINGTON — After being ousted from power last July, Egypt’s Muslim Brotherhood, the Arab world’s original Islamist movement, faces an existential moment. The group has been targeted with extreme repression, prompting a wave of commentary about the failure — or even death — of political Islam.

Premature obituaries of the Brotherhood usually turn out to be just that. As early as 1963, the political scientist Manfred Halpern wrote that secular nationalism had triumphed over political Islam. Half a century later, the Brotherhood’s opponents hold out hope that President Mohamed Morsi’s demise wasn’t that of a man or an organization, but of a worldview. They point to the incompatibility of Islamism and democracy, an odd claim considering that it was the democratically elected Mr. Morsi who was overthrown by the army and not the other way around.

Mr. Morsi was a failure, and he was ousted with the backing of millions. He was stubborn, incompetent and failed to govern inclusively. But there is a different, deeper failure, one that is likely to plague the region for decades to come: the fundamental inability of secular state systems to accommodate Islamist participation in the democratic process.

Americans tend to see liberalism and democracy as going hand in hand. But in the Middle East, democratization, contrary to academic and popular wisdom, is likely to push Islamist parties toward greater illiberalism.

In religiously conservative societies, there is widespread support for more mixing of religion and politics, not less. In Egypt, for example, available polling data makes clear that majorities support Shariah, or Islamic law, as the primary or only source of law; religiously derived criminal punishments; gender inequality; and a role for religious leaders in drafting legislation. If the popular demand is there, someone will need to supply it. Moreover, democracy means that groups like the Brotherhood no longer have a monopoly on the votes of the Islamist faithful. They have to compete with newly established Salafi parties that believe in a strict, literalist Islam, producing a “Tea Party effect” where the center-right is dragged further rightward.

This poses a thorny question for Western observers: Do Arabs have the right to decide — through the democratic process — that they would rather not be liberal?

Even in Tunisia, perhaps the lone bright spot of a now-faded Arab Spring, this issue is far from resolved. The Islamist Ennahda party deserves credit for voluntarily stepping down from power in the face of opposition protests. The true test for Tunisia, however, is still to come. What if Ennahda keeps winning elections and becomes emboldened to pursue the Islamist agenda its conservative base wants it to? Is this something secularists are willing to accept?

During a fragile democratic transition, Ennahda opted not to venture into more divisive territory. But this doesn’t mean that its leaders decided to give up their ultimate, animating objectives. They are Islamists for a reason, after all.

This is the Middle East’s difficult twist. For secularists and liberals, certain rights and freedoms are, by definition, nonnegotiable. They envision the state as a neutral arbiter that stays out of the private lives of its citizens. On the other hand, even the most “moderate” Islamists want the state to promote a basic set of religious and moral values through the soft power of the state machinery, the educational system and the media. As one of Ennahda’s “hard-liners,” Sheikh Habib Ellouze, told me in February 2013: “There aren’t any of us who do not believe in the rulings of Shariah. All of us believe in banning alcohol one day. What we disagree on is how best to present and express our Islamic ideas.”

Liberals would say that their solution is the only acceptable compromise. In a liberal society, everyone — secular and Salafi alike — can freely express their religious preferences. But the notion that liberalism is “neutral” can be accepted only within a liberal framework.

Islamists cannot fully express their Islamism in a strictly secular state. The feelings of alienation that a liberal might feel in a hypothetical “Islamic democracy” are probably not too dissimilar from what the Ennahda leader Rachid Ghannouchi felt when he lived in France as a young graduate student. “The one year I spent in Paris was the hardest and most trying in my entire life,” he wrote in his diary. In his most comprehensive work, “Public Liberties in the Islamic State,” Mr. Ghannouchi attempted to bring Islamic political theory in line with modern democratic norms, but, even here, he falls well short of liberal democracy. This shouldn’t be so surprising: Islamic democracy, however vague, is supposed to rely on a fundamentally different philosophical basis.

If elected Islamist parties have to give up their Islamism, then this runs counter to the essence of democracy — the notion that governments should be responsive to, or at least accommodate, public preferences. Asking Islamists to concede who they are and what they believe is also unsustainable and perhaps even dangerous, pushing conservatives outside the political process.

The implications are clear, if somewhat unsettling. For democracy to flourish in the Middle East it will have to find a way to truly incorporate Islamist parties and, by extension, it will have to be at least somewhat illiberal.

To be sure, in Western Europe and Latin America, socialists and Christian Democrats had to move to the center if they wanted to win elections. But that’s because there was a center. Even in Turkey, which can claim more than 40 years of democratic experience, a strong center has failed to materialize and, if anything, has grown weaker in recent years.

The ideology and ideas of Islamists need to be taken seriously as something deeply and honestly felt. Islamist movements do, in fact, have a distinctive worldview and vision for their societies. If anything, what their detractors say is at least partly true (and it’s something that many Islamists themselves will admit in private): There is, in fact, a “politics of stages” — you concede your Islamist objectives in the short term to strengthen your hand in the long run.

But, as troubling as this may be for Arab liberals, mainstream Islamist movements have been and are likely to remain committed to a democratic process. The scenario of Islamists coming to power through democratic elections only to end democracy has never actually happened. Nor are their beliefs necessarily antithetical to pluralism; Brotherhood-like groups approach Islamic law with flexibility. Far from being textual literalists, their illiberalism tends toward the vague, populist variety. And they’ve come a long way from the 1960s and ’70s, when they saw democracy itself as a foreign import.

This is likely to provide little solace to those who see Islamists, whatever their democratic commitments, as an existential threat. If it is in fact a zero-sum battle, then the other option is to marginalize Islamist parties or eliminate them altogether, which the military-backed regime in Egypt is currently attempting. Such an effort, which many regime supporters see as a necessary evil, is not only bloody and destabilizing but also a fool’s errand. You can try to kill an organization, but killing an idea is a different matter entirely.

Arab autocrats have convinced themselves that past failures to crush the Islamist opposition are a result of not enough force, rather than too much. This latest attempt, backed by Gulf billions and striking levels of repression in Egypt, presents perhaps the most daunting challenge for Islamist movements across the region. But this, too, will fail.

The lesson of the Arab Spring isn’t that Islamist parties are inimical to democracy, but that democracy, or even a semblance of it, is impossible without them. When there are democratic openings — whether that’s in 5, 10 or 15 years — Islamists might look different and talk differently, but they will still be there, waiting and ready to return to political prominence, and perhaps even power.

Shadi Hamidis a fellow at the Brookings Institution’s Saban Center and the author of “Temptations of Power: Islamists and Illiberal Democracy in a New Middle East.”